1. Field of the Invention
The present invention relates to a lens driving device for a zoom or a multifocus lens housing of a camera.
2. Related Background Art
Hitherto, in order to smoothly rectilinearly move a zoom or a multifocus lens, a lens driving device has been arranged in such a manner that there are provided a guide member for rectilinearly guiding the lens and a supporting member for supporting the guide member, and the guide member and the supporting member are arranged to be movable.
FIGS. 1, 2A and 2B are schematic views which respectively illustrate an example of the above-described structure.
A roller 1 serving as the support member is placed within a groove hole 2 formed in a guide member 3. Since the roller 1 is arranged to be capable of freely rotating, an excellent driving efficiency can be realized in comparison to a structure in which a pin is employed. Furthermore, the lens can be rectilinearly moved without a play or a catch even if excellent parallelism between the guiding direction and the optical axis and the accuracy are not realized.
However, the above-described conventional structure has a problem in that, in a case as shown in FIG. 2A in which the guide member is arranged to be a fork-like shape, the parallelism of the two side surfaces of the groove hole 2 in the guide member 3 which is positioned in contact with the roller 1 cannot be maintained by the side pressure given from the roller 1 when the lens is rectilinearly moved. As a result, the two end portions of the fork-like guide member 3 are undesirably opened, causing the accuracy in the guiding action to be deteriorated and a play to be generated. In order to overcome this problem, a structure has been employed in which the groove hole 4 is, as shown in FIG. 2B, closed. However, it leads to a fact that the length and the size of the guide member cannot be reduced. Therefore, the conventional technology encounters a problem in that a desire to reduce the size and the thickness of the camera for the purpose of realizing a collapsible lens housing cannot be met.
Hitherto, as light shielding means, a structure has been employed in which a light shielding member made of rubber, paper, or woven fabric is secured to a camera body or a lens housing at, for example, the inner helicoid by an adhesive or the like so as to cover the gap.
As an alternative to this, a rubber washer is inserted between the camera body and the lens housing for the purpose of covering the gap in such a manner that it is not fixed.
The above-described light shielding structure of a type in which the light shielding member is secured to the inner helicoid encounters a problem in that, if there is an eccentricity generated between the inner helicoid and the lens housing due to manufacturing or an eccentricity generated due to the assembling work or the adjustment work, a gap is formed due to the thus generated eccentricity, causing light to be leaked. If the light shielding member is strongly abutted against the inner helicoid for the purpose of preventing the light leakage, an excessively large resistance arises at the time of the rectilinear movement of the lens housing, causing a load necessary to drive the lens housing to be excessively enlarged.
In the case where the rubber washer is inserted between the camera body and the lens housing in such a manner that the washer is not fixed, the light leakage due to the above-described eccentricity can be prevented. However, a gap is formed with the inner helicoid when the lens housing is moved, in particular, when the same is forwards moved. In particular, light travelling in the direction except for the direction of the optical axis leaks.
Furthermore, in a camera of a type arranged in such a manner that an electric device including a CPU, a collimator and a photometer and the like is provided in the camera housing and an electric device including a shutter operating portion and a focusing device and the like is provided in the lens portion, a flexible print substrate (to be called an "FPC" hereinafter) for establishing the connection between the above-described two electric devices is accommodated in the lens housing in a spiral or folded manner.
In the above-described conventional structure, the FPC is not insulated from the inside portion of the lens housing. Therefore, the FPC has an exposure portion confronting the optical axis, causing the surface of the FPC to reflect the diffused light. As a result, a problem in terms of a ghost image takes place. Accordingly, coating or tape application becomes necessary in order to prevent the light reflection, causing the manufacturing cost to be raised.
Furthermore, there has been a fear of introduction of the FPC deflected into the optical path, causing the travel of the light beam to be obstructed. If the above-described problem is prevented by a design arrangement, the FPC must forcibly be bent or deflected so as to realize the above-described arrangement. As a result, the FPC is applied with excessively large force, causing the durability to be deteriorated.
Hitherto, a variety of cameras each of which has a barrier have been known which is arranged in such a manner that the forward end of the imaging lens is selectively capped by a barrier which is arranged to be optionally opened/closed. A barrier of the type described above is effective to protect the imaging lens from a damage due to an undesirable contact with an external substance or an adhesion of dust or the like. Furthermore, the above-described structure reveals an advantage in comparison to a lens cap employed in ordinary cameras since the fear of missing can be prevented. Therefore, it is preferable that a barrier of the type described above be employed in compact cameras.
As a camera with a barrier of the type described above, a collapsible type camera has been known. A collapsible type camera of the type described above usually employs a barrier opening/closing mechanism capable of automatically opening/closing the lens protection barrier in synchronization with the retraction/protraction action of the lens housing which holds the imaging lens. The reason for this lies in that it is advantageous in terms of operation and handling that the barrier is automatically opened/closed in synchronization with the movement of the lens housing since the lens housing is retracted in the camera housing when a picture is not taken and the lens housing is protracted from the camera housing when the picture is taken.
Although a variety of disclosures have been made relating to the barrier opening/closing mechanism for use in a collapsible type camera with the barrier of the type described above, a structure revealing both an extremely simple structure and easy handling has not as yet been disclosed.
For example, a barrier opening/closing mechanism has been disclosed in U.S. Pat. No. 4,864,338 which is arranged in such a manner that, when the lens housing is retracted, a portion of a barrier opening/closing member, which is arranged to be moved in synchronization with the movement of the lens housing, is engaged with a cam surface of an engagement member provided in the camera housing so that the barrier is closed. That is, the above-described barrier opening/closing mechanism is arranged in such a manner that a slide lever is provided for a transmission shaft which projects from the barrier opening/closing member disposed adjacent to the lens housing toward the camera housing. The slide lever is arranged to be selectively engaged with the cam surface of the engagement member disposed in the camera housing. The portion including the slide lever is forcibly rotated by the cam surface against the urging force of a spring which always urges the barrier in the opening direction. As a result, the barrier is opened/closed via the barrier opening/closing member including the transmission shaft.
The above-described conventional barrier opening/closing mechanism is arranged in such a manner that the slide lever which is urged by the simple tension spring in a direction in which the barrier is opened and the cam surface having a simple slope are engaged to each other so that the movement in the direction of the optical axis of the lens is converted into a rotary motion. Therefore, the structure is not provided with means for preventing a change in the urging force of the spring acting on the slide lever. As a result, a problem arise in terms of a practical use. That is, the urging force of the spring is determined by the length of its elongation in accordance with the degree of the rotation of the slide lever, the spring acting on the slide lever which is engaged to the cam surface so as to be rotated while moving in synchronization with the rectilinear motion of the lens housing in the direction of the optical axis of the lens. As a result, the quantity of force (driving force) necessary to rectilinearly move the lens housing at the time of opening/closing the barrier becomes inequal. Therefore, a user feels uneasy because the retraction/protraction action of the lens housing cannot be smoothly performed. In particular, since collapsible cameras of the type described above usually use an electric motor so as to retract/protract the lens housing, the above-described inequal force causes the load of the electric motor acting on the lens housing driving system to be changed. Therefore, a problem arises in that vibrations and noise generated in the motor and/or the gear configuration and the change in the driving speed of the lens housing can be perceived by a user. What is even worse, if the battery has been consumed, the output from the motor is lowered excessively, causing the lens housing to be stopped at an intermediate position. The change in the moving force exerts a bad influence upon the mirror housing driving system and the cam engagement portion. In particular, a partial and eccentric wear will deteriorate the durability, causing a critical problem to take place when used practically.
In particular, the above-described lens housing driving system and the barrier opening/closing mechanism must be able to smoothly operate while preventing the change in the load to be applied to the lens housing. In addition, there has been a desire to improve the durability of each of the above-described system and the mechanism. Thus, there arises a necessity of providing a structure capable of overcoming the above-described problems.